An Introduction toAkka and the Actor-Based Model

Daniela Sfregola

@DanielaSfregolahttp://danielasfregola.com/

Scala Italy 2015

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Outline

ConcurrencyThread-Lock-Monitor ApproachMessage-Passing ApproachAkka as Message-Passing FrameworkActors in AkkaActor Life CycleActors HierarchySupervision RulesDemo

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Motivation: Concurrency

Multiple Core CPUsDistributed SystemsLow Cost HardwareParallelism

We need to deal with shared resource between processes!

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Thread-Lock-Monitor Approach

Thread-Lock-Monitor approach can be challenging:

Logic complicated for humansDifficult to design and maintainHigh unpredictability

Do we have an easier approach to tackle concurrency problems?

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Message-Passing Approach

The Message-Passing Approach:Encapsulates all the shared information in messagesMessages are used to communicate between processes

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Akka as Message-Passing Framework

Akka - from akka.io

Build powerful concurrent & distributed applications more easily.

Simple Concurrency & DistributionResilient by DesignHigh PerformanceElastic & DecentralizedExtensible

It supports Scala, Java... .NET is coming soon!

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Actors in Akka

Lightweight concurrent entityEvent-drivenMailbox of messages processed asynchronouslyCan hold status/mutability

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Actor Life Cycle

Akka in action (2013) by R. Roestenburg, R. Bakker and R. Williams.Shelter Island: Manning Publication

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Actors Hierarchy

from http://doc.akka.io/docs/akka/snapshot/general/supervision.html#supervision,accessed on May 2015

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Supervision Rules

Your Father is your SupervisorEvery Actor has a Supervisor, but the Guardian Actor (/user)Your Children follow your destinyIf unable to handle an exception, escalate it to your SupervisorIf the Guardian Actor is unable to handle an exception, the systemwill shutdown

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Actor Core Operations

There are four core operations on Actors:

createsendbecomesupervise

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Demo

Demo Time!

Gist available athttps://gist.github.com/DanielaSfregola/6dc52bffa2ed566de9b2

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Conclusions

Akka as Message-Passing approach to concurrencyMain components: ActorsBest Practices:

Never BlockCommunicate only via messagesMessages should be immutableMessages should be complete and self-contained

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Conclusions

Akka as Message-Passing approach to concurrencyMain components: ActorsBest Practices:

Never BlockCommunicate only via messagesMessages should be immutableMessages should be complete and self-contained

Thank you!

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